Switching stage with mos crosspoints

ABSTRACT

A switching stage is provided which employs multiselectors formed by MOS crosspoints. The operations of path search, subscriber test and call detection are made by a cyclic exploration of all the possible paths between a junctor and one (or all) subscriber(s). The supervision data (&#39;&#39;&#39;&#39;off-hook&#39;&#39;&#39;&#39; condition and &#39;&#39;&#39;&#39;path established&#39;&#39;&#39;&#39; condition) are obtained by monitoring the DC levels on the two speech conductors.

liit tent lnventors Marc Jean Pierre Leger lssy-les-Mloulineann;

Claude llaul lHlenri Lerouge, Maurepas; Marc Andre Regnier,Aulnay-sons-Bols, all

011 France Appl. No. 834,673 Filed June 19, 1969 Patented Dec. 7, 1971Assignee lnternational Standard Electric Corporation New Yorlr, NY.Priority June 25, 1968 France 1564105 SWl'llCHlNG STAGE WllTl-l MOSCROSSPOIINTS Primary ExaminerWilliam C. Cooper Attorneys-C. CornellRemsen, Jr., Walter J. Baum, Paul W. l-lemminger, Charles L. Johnson,Jr., Delbert P. Warner, James B. Raden and Marvin M. Chaban ABSTRACT: Aswitching stage is provided which employs multiselectors formed by MOScrosspoints. The operations of path search, subscriber test and calldetection are made by a cyclic exploration of all the possible pathsbetw een a junctor and one (or all) subscriber(s) The supervision data(off- 6Claims, 171Drawing1 igs. hook" condition and path established"condition) are obth D us. Cl 179/1815111 22: by C levelsmthetwospeechConduc lnt.Cl 1104i 3/00 Field of Search 179/18GF Information ConductorsI I H H!) Holding Flip-Flap W/ PATENIEB DEC 7 I971 SHEET 3 OF 6 PATENTEUDEE 719m SHEET *4 [IF 6 PATENTED DEB 7:971

SHEET 5 BF 6 JICD SWITCHING STAGE WITH MOS CROSSPOINTS The presentinvention concerns a switching stage comprising electronicmultiselectors, the contacts of which are constituted by metal-oxidesilicon field-effect transistors or MOS transistors and more generallyby active quadripoles crosspoints which can be realized in large-scaleintegrated circuits. Besides, the present invention concerns also aparticular way of carrying out elementary operations in a switchingstage, these operations being-in the case of a telephone centralexchange-path release, the path search, the call detection and calledsubscribers test.

in the French patent and the applications for certificates of additionto said patent which are listed hereafter, several examples ofachievement of an elementary multiselector carried out in integratedcircuits have been described. These applications, deposited by theapplicant and entitled Electronic Multi-Selector are:

a. Patent application No. PV 131 905 deposited on 12th Dec. 1967 (M. J.P. Leger-C. P. H. Lerouge-J. H. Dejean 3-1016, now French Pat. No.1,555,813, corresponding to U.S. Pat. application No. 788,]14 filed Dec.5, 1968.

b. First patent of addition certificate No. PV 150 086 deposited on 30thApr. 1968 (P. Girard-M. .l. P. Le'gerC. P. H. Lerouge-J. H. De'jean-444-17) c. Second patent of addition certificate No. PV 152 195deposited on 17th May 1968 (J. M. Hennes--M. .l. P. Le'ger- C. P. H.Lerouge l-5-15).

ln the present invention, elementary multiselectors of the typesdescribed are grouped according to lines and columns in order to obtainmultiselectors having relatively large capacities (for instance, from 64to 256 cross-points) and which are assembled in such a way as toconstitute several selection stages.

If the switching stage comprises n selection stages, a path between asubscribers line and a junctor comprises n MOS transistors connected inseries which are coupled to these equipments via bipolar transistors.Since the reverse voltage transfer ratio hl2 of these transistors isextremely low, such a path can assure only an unidirectionaltransmission, and each contact element located at a cross-point mustcomprise two transistors MOS in order to assure the bidirectionaltransmission of the speech signals.

In the present invention, these two paths are used for signaling onebeing used for transmitting a signal meaning that the subscribers set iseither on-hook or off-hook, and the other being used for transmitting asignal characterizing the fact that a path is set up between a giveninput equipment (subscribers line) and output equipment (junctor).

The two contact elements associated with each cross-point are placed ina switching circuit comprising the following output conductors:

Vertical selection conductor d,

Horizontal selection conductor s,

Line conductor e.

ln a multiselector, the conductors d of all the switching circuitsassociated to a vertical j are connected together and are brought to oneof the two potentials characterized by the logical condition D or D andthe conductors s (e) of all the switching circuits associated to anhorizontal k are connected together and are brought to one of Lhe twopotentials characterized by the logical condition S or S (E or E).

The control of the switching circuit Xjk placed at the intersection ofthe vertical j and of the horizontal k is carried out as follows:

a. Horizontal selection: a selection signal S is applied to theconductor s;

b. Opening of the contacts: a signal D is applied to the conductor d;

c. Closing of the contacts, which can take place only if a free linesignal E is present: the vertical selection conductor potential isswitched; the signal D being replaced by the signal D. When the contactsare closed, a busy signal E appears on the line conductor e.

in a switching stage according to the invention and comprising severalselection stages, the speech and line conductors of each horizontal of astage Tp are connected to the speech and selection conductors of avertical of the preceding stage T(p-1. It results therefrom that theswitching of potential over the conductor e of the circuit Xjkconstitutes the closing signal applied to the vertical of the stageT(p-1) to which this conductor is connected and that a path is set upthrough the switch by the closing in cascade of n: switching circuits(one circuit per selection stage) if the corresponding horizontalsselected previously by signals are free.

The various elementary operations stated hereabove are performed, ineach of the selection stages, either by the selection of a givenhorizontal, or by a cyclic selection of all the horizontals, this latteroperation enabling to test all the possible paths connecting the stageTp to the stage T(pl The object of the present invention is thus torealize a switching stage equipped with electronic multiselectors.

A feature of the invention is that each multiselector is realized by theassociation, along verticals and horizontals, of a plurality ofelementary multiselectors, each one comprising several switchingcircuits in matrix arrangement, that each switching circuit comprisestwo MOS transistors as contact elements placed between two horizontalspeech conductors, and two vertical speech conductors and that each ofsaid circuits comprises, as output conductors, a vertical selectionconductor 11, an horizontal selection conductor s, and a line conductore.

Another feature of the invention is that in a multiselector, theconductors d of all the circuits associated to a vertical j areconnected together and are brought to one of two potentialscharacterized by the logical conditions D and D, that the conductorss(e) of all the circuits associated to an horizontal k are connectedtogether and are brought to one of two potentials characterized by thelogical conditions S and S (E and E), that, in order to close theswitching circuit Xjk, first one carries out the selection of thehorizontal k by applying a signal to the conductor s, second, one opensall the circuits associated to the vertical j by applying a signal D tothe conductor d, third, one switches the potential appfled on thisconductor by replacing the signal D by a signal D, which closes thecircuit Sjk if a signal E is present on the conductor e, this signalcharacterizing the fact that no circuit at all is closed on theconductor k and that a signal E appears on this conductor, upon theclosing of this circuit, the signals D and E (D and E) having the sameamplitude.

Another feature of the invention is that the switching stage comprises,in the case of a telephone exchange, an input stage Tx which groups thesubscribers lines, three selection stages Ta, Tb, Tc, assuring thetraffic concentration and an output stage Ty grouping the junctors, thatthe speech and line conductors of each horizontal of one stage, To forinstance, are connected respectively to the vertical selection andspeech conductors of one vertical of the preceding stage Tb so that theswitching of the potentia] over the conductor e of the circuit Xjk(passage from E to E) constitutes the closing signal applied to thevertical of the stage Tb to which this conductor is connected, and thata path is set up automatically through the switching stage if thecorresponding horizontals, previously selected by signals S are free.

Another feature of the invention is that each selection stage comprisesseveral identical multiselectors the homologous horizontal selectionconductors of which are connected together and receive their signalsfrom decoders associated to three counters, Ka, Kb, Kc and that the twospeech conductors are used for obtaining, in each junctor such as Vz,signalling informations Ru and Rb characterizing the fact that,respectively, the input equipment identified by the codes stored in thecounters Ka, Kb is in the off hook" condition and that a path is set upbetween the subscriber identified by these codes and the junctor Vz.

Another characteristic of the invention lies upon the fact that for thepath searching and for the subscribers line test which consist insearching, starting from a junctor Vz, a path between this junctor and asubscriber identified by the codes stored in the counters Ka, Kb onescans all of the possible paths by a cyclic advance of the counter Kc,that at each position of the counter a path may be set up in cascadethrough the stages Tc, Tb, Ta, if the selected horizontals are free, andthat, when such a path is set up, the logical conditions of end ofoperation are the condition Rb for the search of a path and thecondition Rb, Ra for the subscribers line test.

Another feature of the invention is that, for the call detection, thecounters Ka, Kb, Kc are connected in series and receive signals whichcontrol their cyclic advance so that all the input equipments areexplored successively from the junctor Vz and that the apparition of asignal It: indicates that the equipment identified by the codes storedin the counters Ka and Kb is calling.

The above-mentioned and other features and objects of this inventionwill become apparent by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1 represents a MOS transistor switching circuit;

FIG. 2 represents a symbolic diagram of this circuit;

FIG. 3 represents a complete matrix of multiselector;

FIG. 4 represents an example of a switching stage;

FIG. 5 represents the logical circuit of a junctor;

FIG. 6 represents the state detector;

FIG. 7 represents the various connections between the junctors, theswitching stage and the centralized control circuit;

FIGS. 8a to 8 represent diagrams of signals.

The mode of operation of a switching circuit and the organization of amultiselector matrix, such as they have been described in theapplication for a patent of addition referenced (b) hereabove will befirst described.

FIG. 1 represents this switching circuit wherein all the components are,by way of a non limitative example. MOS transistors and which comprises:

The MOS-Pk transistor referenced T which acts as a contact between theinformation conductors H and V,

The holding flip-flop W the 1 outlet of which is connected to the gridof the transistor T and to the conductor w. It is also realized withMOS-Pb transistors and it either blocks or makes conductive thistransistor according to whether it is in the 0 or I state. Thisflip-flop is reset to the 0 state by a signal D applied to the conductord.

The three-input NOR gate P connected to the conductors d, s, e and whichcontrols the setting to the I state of the flipflop W when signals D Eare applied respectively to these conductors, viz in logical notation:

r 35PL+ ff liiif. The signal D is obtained from the signal D inverted bythe circuit L and one uses the fact that there exists a slight delay tobetween these two signals, which is due to the rise time of the signalin the circuit L.

represents a multiselector comprising n horizontals HI, H2...I-In and mverticals V1, V2...Vm. A switching circuit has been placed at eachcross-point, those associated to the horizontal H1 being referenced X11, X21...Xml and those associated to the vertical Vl being referenced XI1, XI2...XIn.

The matrix comprises besides a logical circuit per horizontal, viz forthe horizontal H1, the circuit G1 comprising the NOR-circuit 0'1 and theinverter G"l. The circuit GI comprises m inputs WIl, W21...Wml connectedto the conductors W (output I of the flip-flops W, FIG. I) of theswitching circuits associated to the horizontal HI. It is thus seenthat:

The circuit G'l delivers over the conductor el a signal El for thelogical condition: E l=Wl I+W2I+... Wm 1.

The circuit G"l delivers over the conductor e'l a signal EI for thelogical condition: E I=Wl 1+." W I.

The presence of the signals El and El thus means that at least oneswitching circuit associated to the horizontal H1 is closed. Thesesignals will be called busy signals and the signals E 1 and IE] will becalled free signals.

The table I herebelow groups the various signals applied to the controlconductors of a switching circuit. It will be noted that the verticalselection signal is the normal signal D whereas the horizontal selectionsignal is the complemented signal TABLE L-CONTROL AND BUSY SIGNALSConductor Signal Voltage D -U Vertical selection signal.

{5' 0 Delayed vertical selection signal.

{ 0 Horizontal selection signal.

0 }Free signals. e E -U o, E Bus si ncls. e E 0 y g We shall now brieflydescribe, with the help of table II, the method of control of theswitching circuit Xjk placed at the intersection of the vertical Vj andof the horizontal PM. We shall assume that the cell is initially in thestate of rest, i.e. that signals and Sk are applied to the selectionconductors and that the horizontal I-ik is free, i.e. that a signal Ekis applied to the conductor e'k (see table II, line a).

The control of the closing of the circuit Xjk is carried out byperforming successively the following operations:

I--Horizontal selection (see table II, line b): A voltage U is appliedto all the conductors s1 to sn with the e zeption of the conductor skwhich must be grounded (signal Sk). Since a signal D'j is present, thegate Pjk of the circuit Sjk is blocked and the flip-flop Wjk of thecircuit Xjk does not switch (see FIG. 1).

2-Vertical selection (see table II, line c): A signal Dj is ap- TABLEII.-CONIROL OF THE SWITCHING CIRCUIT Xjk Conductors Operation (1 d s e pFlipflop W a R st I? 0) D'j s k E: 0 3T5 W]k0r V V iT b... Horizontalselection Di (0) D (-U) E15 (0) if (0) Pjk Wjk or Wjk c... Verticalselection (-U) (0) S k (0) it (0) Pjk Wjk d. Closing l2 (0) D'j (0) it(0) Ek (0) Wjk 0.... Holding Di (0) D'j (-U) Sk or Sk Ek (-U) Pjk Wjk;"which is required in a telephone exchange. Thus, FIG. 3

plied to the vertical selection conductor dj so that the flip-flop Wjkreceives a signal of resetting to the 0 state (condition W711) as wellas all the other flip-flops associated to the ertical Vj. After a delayto, the circuit Lj delivers a signal D'j a i, since the horizontal isfree (signal I??? and selected (signal Sk) the gate Pjk is energized(signal Pjk). The flip-flop Wjk receives thus a signal on its twocontrol inputs and remains in the 0 state.

3Closing of the cross-point: The signal Dj (condition Dj) is suppressedbut the signal is still present during a time to. The gate Pjk remainsthus energized so that the flip-flop Wjk sets to the I state (table II,line d) so that both transistors which act as contacts are conducting:the switching circuit is closed.

After a time to, a signal Dj appears, which blocks the gate Pjk and thecircuit remains closed (table ll, line e).

4-End of operation: A modification of the state of the circuit Xjk canonly take place atterwards if a signal 1)] is applied. One may thusallow the application of the signal Sic as long as a new circuit has notto be selected in the matrix.

After having recalled the constitution and the operation of amultiselector including MOS transistor switching circuits, we shalldescribe a telephone exchange according to the invention, whichcomprises a switching stage wherein the switching circuits arecontrolled by orders Qa, Qb, Qc, Qd (see table V, columns a and b)delivered by the centralized control circuit CP, the organization ofthis circuit being such as one single order is performed at a time.

FlG. 1 represents such a switching stage and table III describes itscomposition.

P10. 5 represents the logical circuit JLMM of the junctor V1041associated to the multiselector all of the selection stage To as well asthe multiselector b6 of the stage Tb.

On this figure, one has shown a path set up through the switchingcircuits X1713 and Xcdo, the small letter characterizingin thesereferencesthe selection stage, the first digit the number of thevertical and the second digit the number of the horizontal.

It will be noted that the links between b6 and c1 and between c1 andJlLltMi comprise two speech conductors drawn in plain lines and aselection conductor drawn in thin lines.

The circuit JLltMl comprises:

The state detector ST to which are connected the two speech conductorsand which supplies a loop signal Rb and a path signal Rb for theconditions shown in table lV. FIG. 6 shows the detailed diagram of thiscircuit ST.

TABLE IV: Operating conditions TABLE IIL-COMPOSITION OF THE SWITCHINGSTAGE D Signal Condition Horizontal Stages Composition selection signalsLoop signal In Off-hook condition Input Stage TX'" g fig gfig E1011 2.5Ra On-hook condition or normal H601 H1616: connection or internalblocking First selection 16 Multiselectors a1, a2 Sal, SaZ Salli PathSignal Rb Path established bclww i stage Ta. s16 fonpriising cattiih 116horiand a subscriber's set Zen 9. an 8 ver es s. R?) Noncstabilished athSGCQnd Selection 8 multiselectors b2 b8 S132 Sbs Answer signal Rb XII nCalled subscriber which is free and can stage Tb. corcrlrgglsing eatlir16 horizontals be confined an vertica Third selection 16 multiselectorsc1, c2 (:16 S01, S02 Sc8 stage Tc. comprising each 8 horizontals and 8verticals. Output stage Ty. 128junctors V101 V104 V116 V1601 V1616.

The links between the various selection stages are connected in awell-known way. Thus the horizOntals H1 to H16 of the multiselector b 1are connected to the verticals V1 of the multiselectors al to a116, thehorizontals of the multiselector b2 are connected to the verticals V2 ofthe multiselectors al to 1116, etc. In the same way, the horizontals ofthe multiselector C1 are connected to the verticals V1 of themultiselectors b1 to bfi etc....

The horizontal selection signals of table III are delivered in eachselection stage by a selector comprising, for the stage Ta for instance,the counter Ka and the decoder Sa. By means of these selectors which maybe connected in series by the activation of the gate P12, one performs acyclic selection of all the horizontals of the switching stage byapplying a train of pulses Gt at the input of the counter Kc. One mayalso select, in any one of the stages Ta and Tb, a given horizontal ineach one of the multiselectors by introducing, in the counters Ka andiib, the corresponding codes C and Cb. It will be noted that such a pairof codes identifies, by a matrixtype selection, one of the subscribersconnected to the exchange since the code Ca defines the horizontal inone of the multiselectors al to 016 and that the code Cb defines one ofthese multiselectors al to alto.

The output stage Ty comprises 128 junctors which may be of threedifferent types:

l--The local junctor comprising two junctors such as V101 and V1601connected by the speech conductors and which enables the setting up of aconnection between two subscribers.

2-The outgoing junctor such as V104 which enables the setting up of aconnection between a subscriber and the outgoing trunk 1C1.

3The digit receiver V116 which is connected to a subscriber for thenumber reception.

All these types of junctors are connected to the centralized controlcircuit CP for performing data transfer operations. Thus, for instance,the digits decoded in the receiver V116 are transmitted to the circuitC? which stores them in a register.

The order control circuit DC comprising several logical circuits usedfor controlling the execution of the orders Qa, Ob, 00, 0d. The logicalconditions are shown in table VI.

FIG. 15 represents the detailed diagram of a path established between asubscribers line and the state detector ST of a junctor of the outputstage Ty. This path enables to set up a bidirectional speech connectionfrom T1: towards Ty (arrow 1, MOS transistors E'a, E'b, E'c) and from Tytowards Tx (arrow 2, M05 transistors E"a, E"b, E"c). The couplingbetween these MOS transistors and the stages T): and Ty is carried outthrough bipolar transistors in common base configuration Txll, Tyl, TxZ,TyZ. The holding flip-flops W of HO. 1 have been shown symbolically bythe changeover switches Wa, Wb, We which apply to the grids either theground potential (blocking of the transistors) or the potential 24 volts(conducting transistors).

The three MOS transistors of each chain are equivalent to a resistanceof 600 ohms, for instance, when the switches are closed.

On the chain 1, supplied by -24 volts and +12 volts, the switch Z1represents the hook of the set which is in the position Off when thislatter is unhooked and in the position On when it is hooked. The chain 2is supplied between +12 and 24 volts.

On this figure, the voltages shown. in an oval are those present foreach chain when the path is set up, and those shown in a rectangle arethose present when this path is broken. Last, the numbers shown betweenbrackets under a resistance represent the value of this latter in kit.It will be noted that, in order to avoid the decimals, it has beenassumed that a conducting or saturated bipolar transistor had abaseemitter voltage drop of l volt.

The mode of elaboration of the signals Ra and R b will now be describedby choosing a value of direct current, in each chain, equal to 5 ma.when the path is :set up this giving drainsource voltage drop of 1 voltper MOS transistor. One has also chosen a collector-to-emitter voltageequal to or higher than 3 volts for each bipolar transistor.

1Elaboration of the signal Ra (chain 1) When the switch Z1 is in the offposition, no current at all flows in the chain 1, and the collector ofthe transistor Tyl is 2-Elaboration of the signal Rb (chain 2) When theswitch Z2 is open and the switches Wa, Wb, We are grounded no current atall flows in the chain 1, but the base-emitter junction of thetransistor Ty2 is conducting whereas the transistor Ty4 is blocked.

In fact, the bases of these two transistors are brought to 6 voltsthrough the resistor R8 and the emitter of the transistor Ty2 is brought(through R6) to a potential much more negative than the emitter of thetransistor Ty4 so that a current flows in the base-emitter junction ofTy2. The value of the potential of the bases is thus fixed at about 8volts by the resistor bridge R6-R8, this assuring the blocking of Ty4and the presence of a signal Rb.

When the switches Wa, Wb, Wc are in the upper position, all thetransistors of the chain 2 are conducting with the indicated voltagesand, if the transistor Tyyhas a gain fi=50, its base current is 0.1 ma.for a chain current of ma. Since Ty4 is blocked, the base current of Ty2produces a voltage drop of 0.47 0.1 volt in R8, viz a base voltage ofapproximately 5.95 volts which produces the saturation of Ty4 and thepassage of the base voltage to -7 volts. A current of 2.] ma. flows thenthrough the resistor R8 of which 0.1 ma. is absorbed by Ty2 and theremainder by Ty4. One obtains thus a signal Rb of amplitude 8 volts.

The order control circuit DC represented on FIG. 5 comprises theflip-flop M, the OR-circuits P1, P3, P8, P9 and the AND-circuits P2, P4,P5, P6, P7. The control signals of these logical circuits are of threetypes:

a.The signals Gt constituted by a train of pulses of period b.Thesignals Ra and Rb defined previously,

C.The order signals Qa, Qb, Qc, Qd which are delivered by thecentralized control circuit CP. These latter control the differentoperations performed during the processing of a call and which aregrouped in column a of table V.

In order to execute one of the orders Qb, Qc, Qd, in a given junctor,the circuit CP selects this junctor and sends to it the order signal(table V, column b). These order signals are also applied to theswitching stage (FIG. 4) for controlling the advance of the selectorsKa, Kb, Kc by means of the AND-circuits P11, P12 and of the OR-circuitP13.

Thus, for the logical condition (Qb+Qc+Qd), the selector Kc advancescyclically under the control of the signals Gt as indicated table V(column e). The other two selectors Ka and Kb advance cyclically onlyfor the order Or (table V, columns 0 and d).

For the orders Oh and Qd, the horizontal selection in the stages Ta andTb is performed under the control of the codes Ca and Cb sent by thecircuit CP, the set of these two codes identifying-as it has been seenpreviously-one of the equipments of the input stage Tx.

The selection signal of the vertical of the stage Tc associated to theselected junctor is elaborated in the order control cir- TABLE V.CALLPROCESSING TABLE VI.C0NTR011 CIRCUIT ORDER Reference Logical conditionGates (1). Qb+Qc+Qd- M P3 (2) M.Gt=Mt P2 (3)"... Mt-l -2a=D4 P1 (4)Qa.Rb+QERb+Qc.Ra+Qd.Ra.Rb=Xa P4, P5, P6, P7, P8 (5) Xa+Xb- M P9 cuit DCthe operation of which is summarized by the logical equations of tableVI. In these logical equations, the sign means that, when the logicalequation indicated on the lefthand side is satisfied, the flip-flop M isset to the indicated state.

FIG. 7 represents a general diagram of the exchange on which arerepresented the connections between the centralized control circuit CP,the switching stage ST which groups the selection stages Ta, Tb, Tc andthe input stage Tx (see FIG. 4) as well as one of the junctors of theoutput stage Ty, the junctor V104 for instance.

The junctor selection mentioned hereabove is carried out by means of thedecoder JD comprising the outputs V101,...V104...Vl6l6 When a signalappears on the output V104 at the same time as one of the order signals,this signal V104 activates the AND multiple circuit P104 (the stage Tycomprises 128 gates of this type as indicated on the multiplexing arrow)and the order signal is transmitted to the circuit .IL (FIG. 5) of thejunctor V104. This signal is also transmitted, except for the order On,to the circuit ST in which it is applied first to the gates P12 and P13(see FIG. 4) for controlling the cyclic selection during the performanceof the order and second to the AND multiple circuits P14 and P15 usedfor transferring the codes stored in the counters Ka and Kb to thecircuit CP at the end of an order Qc (see table V, column i).

The equation 4 of table VI gives the logical conditions for which anexecution signal Xa appears, ie a signal characterizing the fact that anorder has been satisfactorily achieved. The outputs Xa of all thejunctors of the stage Ty are connected to the inputs of the OR-circuitP22, the output of which is connected first to the AND multiple circuitsP14, P15 (see FIG. 4) of the switching stage ST and second to thecircuit CP.

It is possible that an order cannot be performed satisfactorily becauseof a defective circuit, of an internal blocking (orders Qb, Qd) orbecause its result is negative (order Qd, if the tested subscriber is online). In order to detect these conditions, the circuit CP elaborates asignal Xb which appears when the maximum time of allowed to the order isreached, the durations of the time delays being indicated in column f oftable V. It will be noted that a signal Xb is not associated to the calldetection order since such an operation must be carried out cyclicallyin a permanent way. Nevertheless, provision can be made for an alarmsignal appearing after a certain time of scanning without result andcharacterizing a fault in the circuits.

The signal Xb is applied to the junctor V104 and controls the stoppingof the operation as indicated by equation 5 of table VI.

The processing of the orders Qa, Qb, Qc, Qd will now be described.

In the circuit JL (FIG. 5) the gates P1 to P9 and the flip-flop M aremade up, by way of example, with circuits such as an End of operationCodes Horizontal selections Vertical trans- Operation Order Stage TaStage 'Ib Stage Tc duration tion, Ud cond. to 01? Release Qa To -U it?Puth search Qb a Cb Cyclic T3 Mt BB (all detection Qc Cyclic CyclicCyclic Mt Ra Ca-Cb Subscriber's test Qd Ca Cb Cyclic T3 Mt Rb, Ra,

a b e d o i output signal has a negative potential U of amplitude 12volts and that its complement is represented by the ground potential. Itresults therefrom that when the equation 3 of table VI is not satisfied(condition lit), the vertical selection conductor d4 (FIG. 5) isgrounded. As it has been seen during the study, in relation with thetable II, of the control process of a switching circuit Xjk, this signalassures the holding in the rest state of all the switching circuitsassociated to the vertical whatever may be the signals applied to thehorizontal selection conductors of the multiselector.

1-Release order.

When a release order Qa is received from the circuit CP, the equation 3is fulfilled and the conductor d4 is brought to the potential -U (signalD4) controlling the opening of the switching circuit associated to thevertical V4 which may be closed, and a free signal E of amplitude U (seetable I) ap pears on the conductor e e6 if no circuit at all is closedon the horizontal lHlb. It will be reminded that this conductor isconnected to the vertical selection conductor d l of the multiselectorb6 of the stage Tb (FIG. 41). This signal E controls thus the opening ofthe circuit Xb13 in the manner described previously, and the opening ofthe cross-point which terminates this path in the selection stage Ta: itis thus seen that it is enough to apply a signal Qa to a given junctorfor controlling in a single operation, the release of the path set upbetween this junctor and an equipment of the stage Tx. It will be setthat the maximum duration of this operation is Ta=2".t, t being theduration of one period of the signals Gt (see FIG. do). The end of thetime To is marked, as it has been seen previously, by a signal Xb whichcontrols the setting to the state of the flipflop M.

2Cyclic selection orders.

As indicated in columns c, d, e of table V, the orders 0b, 0c, Qdcontrol the cyclic section of the horizontals in the stages Ta, Tb, Tc.For these orders the equations 2 and 3 show that the voltage on theconductor dd is modulated by the signals Gt between zero and U volts aslong as the equation which controls the resetting of the flip-flop M isnot satisfied.

The orders are performed in the following way:

2.l-Path search. This operation consists in setting up a path, throughthe selection stages Ta, Tb, Tc between an input equipment andidentification codes of which Ca-Cb are supplied by the circuit CP and ajunctor, the junctor V1104 for instance. It will be described inrelation with the diagrams of FIGS. ba to dj.

The order Qb (FIG. 8b) controls the modulation by the signal Mt (FIG.dd), of the potential of the conductor dd, and the first time thisconductor is brought to the potential U, all the switching circuitsassociated to the vertical Vd receive a signal which resets theirholding flip-flops W in the 0 state (see FIG. ll) so that this verticalis released (the signal present on the 1 output of the holding flip-flopWcdb of the circuit X0 56 is shown on FIG. SJ). It will be assumed thatthe decoder Sc (FIG. d) delivers at that time a selection signal S7? ofamplitude zero which starts at time tl (FIG. 8c) in synchronism with thesignal D4 of amplitude U (FIG. 8d). The delayed signal Ddl is shown onFIG. be and it is assumed that the horizOntal H6 is free and that a freesignal E6 is present on the conductor eb (FIG. 8g). Between times :2 andt4 (FIG. 8]) the conductors d4 and (1'4, associated to the vertical V I,are simultaneously grounded (signals fit and 5's At this moment, all theconditions required for the closing of the circuit Xcdfi are assembled(see table II, line d) and the holding flipflop Wcllb of this circuitsets to the 1 state (FIG. Sf) at the same time as the conductor co isgrounded (FIG. bg) which characterizes the fact that the horizontal H6is now busy.

Since the conductor e6 of the multiselector cll is connected to theconductor all of the multiselector be (see FIG. 5) this potentialconstitutes the vertical selection signal of this multiselector in whichit will be assumed that the horizontal H3 is ll Ill flee (signal E3,FIG. tilj) and that it is selected by the signal Sb3 obtained bydecoding the code Cb.

Last, the potential of the conductor dll is shown in the FIG. W1. It isthus seen that, by comparing, the FIGS. fig, tlh II], all the closingconditions of the circuit Xb13 are present between the times 13 and :5(FIG. iii) and, in t5, the flip-flop Wbll3 sets in the I state and thecircuit X1113 is closed.

In the selection stage Ta, which is not shown on FIG. 5, the verticalselection signal is constituted. by the potential of the conductor e3and the horizontal selection signal is delivered by the decoding of thecode Ca.

Since one has to set up a path between the input equipment associated tothis horizontal and the junctor VIM, said horizontal is free and one hasa free signal so that the corresponding switching circuit closes up inthe stage Ta and that the path is set up. The circuit ST (FIG. 5)delivers then a path signal Rb and one has: Qb Rb=Xa (equation 4, tableVI).

As it has been seen above, the signal Xa controls the resetting to the 0state of the flip-flop M (stopping of the modulation on the conductor dtl) and it is transmitted to the circuit CP (FIG. 7) for controlling thesuppression of the order Qb.

If no signal Xa is obtained, the following signal Gr controls theadvance by one position of the selector Kc which delivers thus a signalS77 etc....

If no path is found out after the scanning of all the horizontals in themultiselector C1, i.e. after a duration of T3=2 J (see table V, columnj) the circuit CP sends a signal Xb to the junctor (see FIG. 6) whichcontrols the stopping of the scanning.

2.2-Call detection. This operation consists in scanning cyclically allthe equipments of the stage Tx (FIG. ll) in order to detect those whichare calling. To this effect, one sets up a path between a junctor (V1104for instance) and each of the equipments, a calling equipment beingcharacterized by the supply, by the circuit ST (FIG. 6) of a signal 1%.As it may be seen on FIG. 4, the order 00 activates the gates PM andP12, the cyclic advance of the counters Kc, IIb, Iia which control thusthe scanning of all the possible paths throughout the switching stage.

In the circuit J L (FIG. 5), the potential of the vertical selectionconductor dd is modulated as for the order Oh and, during a scanningcycle of the horizontals of the multiselector cl, the counters I(b andKat show the codes Ca and Cb characterizing a subscriber. This cycle, ofmaximum duration 3!, enables thus to carry out a path search as with theorder Oh for connecting the junctor to this subscriber. If thissubscriber is calling, the circuit ST (FIG. 5) delivers a loop signal mso that a signal Xa appears (equation 4, table VI) which activates theAND-circuits PM, P (FIG. 4i) and controls the transfer of theidentification codes Ca, Cb (FIG. 7) to the circuit CP.

2.3-Subscribers test. This operation consists in setting up a pathbetween a subscriber the codes of which CaCb are given by the circuit CFand a junctor in order to know if this subscriber is free or on line.This operation is thus identical to the path search and it is seen,according to table IV that a free subscriber is characterized by thelogical condition Rb.Ra.

Since the cyclic scanning concerns only the counter Kc, the maximumduration of the operation is 73- 8! and, at the end of this time, thecircuit C? delivers a signal Xb if the condition RbXITa has notappeared, this signal controlling the stopping of the operation.

While the principles of the above invention have been described inconnection with specific: embodiments and particular modificationsthereof it is to be clearly understood that this description is made byway of example and not as a limitation of the scope of the invention.

We claim:

I. A switching stage in which cross-points include metal oxidesemiconductor transistors, said switching stage comprising an inputstage, an output stage, and first and second and third selection stagesplaced between the input stage and the output stage, each of said stagesincluding a plurality of multiselectors, each multiselector including aplurality of horizontals and verticals, and means connecting eachmultiselector horizontal in each selection stage to a vertical of thepreceding stage.

2. A switching stage as claimed in claim 1, in which the multiselectorsin a selection stage include homologous selection horizOntals, and meansconnecting said homologous selection horizontals together to receiveselection signals from a plurality of counters.

3. A switching stage as claimed in claim 1, in which a selectedhorizontal k is free in a selection stage, a switching circuit Xjk atthe intersection of this horizontal and of the vertical j is closed bymodification of the voltage on a vertical selection conductor dj, a busysignal is supplied on the horizontal k and to a vertical of thepreceding stage, whereby a path is set up in cascade between verticalsselected in the selection stages and an equipment in the input stageidentified by the horizontals in the selection stages.

4. A switching stage as claimed in claim 1, in which the switching stageis used in a telephone exchange, two speech conductors are used forobtaining signaling information of a first and a second type, whereinformation of the first type in dicates that the subscribers station isoff-hook and information of the second type indicates that the path isset up.

5. A switching stage as claimed in claim 1, including means forconducting a path search and a subscribers test involving searching apath between an input stage identified by codes in a plurality ofcounters and a junctor connected to a vertical of the third selectionstage, means for scanning all possible paths by cyclically advancing acounter associated with the third selection stage, and means fordetermining when the path is complete between a subscribers set and thevertical of the third selection stage.

6. A switching stage as claimed in claim 5, in which the counters areconnected in series in order to scan all the input equipmentssuccessively, and receipt of a selected signal indicates that theequipment identified by the code on the plurality of counters iscalling.

1. A switching stage in which cross-points include metal oxidesemiconductor transistors, said switching stage comprising an inputstage, an output stage, and first and second and third selection stagesplaced between the input stage and the output stage, each of said stagesincluding a plurality of multiselectors, each multiselector including aplurality of horizontals and verticals, and means connecting eachmultiselector horizOntal in each selection stage to a vertical of thepreceding stage.
 2. A switching stage as claimed in claim 1, in whichthe multiselectors in a selection stage include homologous selectionhorizOntals, and means connecting said homologous selection horizontalstogether to receive selection signals from a plurality of counters.
 3. Aswitching stage as claimed in claim 1, in which a selected horizontal kis free in a selection stage, a switching circuit Xjk at theintersection of this horizontal and of the vertical j is closed bymodification of the voltage on a vertical selection conductor dj, a busysignal is supplied on the horizontal k and to a vertical of thepreceding stage, whereby a path is set up in cascade between verticalsselected in the selection stages and an equipment in the input stageidentified by the horizontals in the selection stages.
 4. A switchingstage as claimed in claim 1, in which the switching stage is used in atelephone exchange, two speech conductors are used for obtainingsignaling information of a first and a second type, where information ofthe first type indicates that the subscriber''s station is''''off-hook'''' and information of the second type indicates that thepath is set up.
 5. A switching stage as claimed in claim 1, includingmeans for conducting a path search and a subscriber''s test involvingsearching a path between an input stage identified by codes in aplurality of counters and a junctor connected to a vertical of the thirdselection stage, means for scanning all possible Paths by cyclicallyadvancing a counter associated with the third selection stage, and meansfor determining when the path is complete between a subscriber''s setand the vertical of the third selection stage.
 6. A switching stage asclaimed in claim 5, in which the counters are connected in series inorder to scan all the input equipments successively, and receipt of aselected signal indicates that the equipment identified by the code onthe plurality of counters is calling.